Effects of Tris Buffer pH Values on the Adsorption of Single-Stranded DNA onto Carbon Nanotubes

Abstract

Carbon nanotubes (CNTs) have attracted considerable attention as nanomaterials for the development of biosensing and molecular diagnostic platforms because of their distinctive carbon-based structure and surface properties. The interaction of nucleic acids with CNT surfaces is influenced by environmental factors, including buffer composition and pH. Tris buffer is widely used in DNA-related applications; however, changes in its pH can modify the chemical environment and consequently affect DNA–nanomaterial interactions. Therefore, this study investigated the effect of Tris buffer pH on the fluorescence response of a single-stranded DNA (ssDNA)–CNT system to identify an appropriate pH for subsequent experiments. ROX-labeled ssDNA was incubated with CNTs in Tris buffer at different pH values, and changes in fluorescence intensity were evaluated as an indicator of DNA–CNT interactions and fluorescence quenching resulting from the proximity of the fluorophore to the CNT surface. In addition, scanning electron microscopy (SEM) was used to examine morphological differences in CNTs before and after interaction with ssDNA. The presence of CNTs resulted in a substantial reduction in ssDNA fluorescence intensity, consistent with the interaction of ssDNA with the CNT surface and the associated fluorescence quenching. Increasing the pH of the Tris buffer resulted in a progressive increase in fluorescence intensity. The fluorescence intensities at pH 4, 5, 6, 7, and 8 were approximately 65, 145, 190, 230, and 355. Among the conditions evaluated, pH 8 produced the highest fluorescence intensity. SEM analysis also revealed observable morphological differences in CNTs following interaction with ssDNA. Overall, these findings demonstrate that Tris buffer pH influences the fluorescence response of the ssDNA–CNT system. Within the investigated pH range, higher pH values were associated with greater fluorescence intensity, indicating that buffer pH is an important experimental parameter to consider when selecting conditions and optimizing CNT-based DNA nanobiosensing platforms.